This application relates to magnetic tape which can be encoded, wound, and subsequently unwound and read from conventional helical spools after exposure at elevated temperatures, e.g. temperatures of from 400.degree. F. to 500.degree. F.
U.S. Pat. No. 3,941,911 to Newton describes e.g., a tape wherein a polymerized polyesterurethane-based magnetic coating is used in conjunction with a polyetherurethane-based backing to achieve what is believed to be the only commercially successful, spoolable, magnetic tape of the prior art which used an organic resin matrix binder for ferromagnetic particles and could withstand high temperatures.
This invention relates to an improvement in the art relating to such high-temperature tapes as disclosed in U.S. Pat. No. 3,941,911. However, whereas the operability of the tape disclosed in that patent was predicated upon assuring a chemical distinction between the matrix for the ferromagnetic facing coating and the matrix for the anti-static carbon black-containing backing coating, the invention described below focuses on a novel, anti-static backing composition which is universally acceptable for use with high-temperature magnetic coatings.
Use of prepolymerized polyesterurethane matrices for ferromagnetic coatings on tape is old in the art. However, most such coatings have been so loaded with lubricants and other plasticizing ingredients that they have little, if any, value in construction of helically spoolable high temperature magnetic tape, except as described in the aforesaid Newton patent. On the other hand, some formulae, and especially the crosslinked formulae disclosed in U.S. Pat. No. 4,020,227 to Deffeyes, do disclose resin binder formulations which, properly cured, have good high temperature properties and may be utilized as high temperature magnetic coatings. More particularly, they can be utilized in helically spooled form when utilized according to the teachings of the invention described below.
In a review of art related to the invention, it is also noted that the use of silicone oil as a lubricant in magnetic tapes is known. It is noted in this connection that this statement of prior art is necessarily prepared in hindsight and nothing herein is to be construed as indicating that there was any basis for assembling this art except in hindsight and with the present invention in mind.